The invention is in the field of electronic reproduction technology and is directed to a method for positioning engraving elements in an electronic engraving machine for engraving printing cylinders for rotogravure, whereby at least two engraving lanes lying side-by-side in an axial direction of the printing cylinder and having predetermined lane widths are engraved with a respectively allocated engraving element, and is also directed to an apparatus for generating reference position marks for the positioning of the engraving elements and to an engraving machine for the implementation of the method.
When engraving printing cylinders in an electronic engraving machine, an engraving element moves along a rotating printing cylinder in the axial direction. The engraving element is designed; for example, as an electromagnetic engraving element with an engraving stylus as a cutting tool. The engraving stylus controlled by an engraving control signal cuts a sequence of cups of different depth arranged in an engraving raster into the generated surface of the printing cylinder. The engraving control signal is formed by superimposition of an image signal that represents the gradations to be engraved between xe2x80x9clightxe2x80x9d (white) and xe2x80x9cdarkxe2x80x9d (black) with a periodic raster signal. Whereas the periodic raster signal effects a vibrating lifting motion of the engraving stylus for producing the engraving raster, the image signal values determine the depths of the cups engraved into the generated surface of the printing cylinder and, thus, the engraved gradations.
For magazine printing, a plurality of stripe-shaped cylinder regionsxe2x80x94called engraving lanesxe2x80x94that lie axially next to one another must often be engraved with a respective engraving element, for example the various printed pages of a print job. The engraving elements allocated to the individual engraving lanes are mounted on a shared engraving carriage that moves along the printing cylinder in the axial direction during engraving.
In order to achieve a good reproduction quality, the axial spacings of the engraving stylus tips of the engraving elements must be set with exact registration onto the required widths of the individual engraving lanes by axial displacement of the engraving elements on the engraving carriage. Subsequently, the engraving carriage with the exactly spaced engraving elements is positioned relative to the printing cylinder such that the engraving stylus tips lie at the axial start position for engraving the engraving lanes.
In order to save time in the exactly registered alignment of the individual engraving elements, an operator first roughly sets the required axial spacings by manual displacement of the engraving elements, for example on the basis of position marks or with the assistance of a measuring tape. The manual rough positioning of the engraving elements saves time, particularly a great number of engraving lanes are to be engraved and, thus, a great number of engraving elements must be positioned. The rough positioning is followed by the exactly registered fine positioning of the engraving elements according to various methods.
An object of the present invention is to specify a method for positioning engraving elements in an electronic engraving machine, an apparatus for generating and displaying reference position marks for the positioning of the engraving elements, as well as an engraving machine for the implementation of the method with which the positioning of engraving elements is facilitated and implemented in the shortest time.
According to the method and system of the present invention for positioning engraving elements in an electronic engraving machine for engraving printing cylinders for rotogravure, at least two engraving lanes having a predetermined lane width lying side-by-side in an axial direction of the engraving cylinder are respectively engraved in the form of cups with a respectively allocated engraving element. Axial spacings of the engraving elements relative to one another before the engraving are set. The engraving elements execute an axial feed motion along the printing cylinder during engraving. For approximately setting the axial spacings of the engraving elements to the lane widths, reference position marks are generated for the engraving elements, the axial spacings of the marks from one another corresponding to the prescribed lane widths of the engraving lanes to be engraved on a printing cylinder. The engraving elements have axial position marks. The engraving elements are axially shifted such that the position marks are in coincidence with the respectively allocated reference position marks.
Advantageous developments and embodiments are recited in the subclaims.
The invention is explained in greater detail below on the basis of FIGS. 1 and 2.